Definitions for "MITM"
an- he- iddle Attack The man in the middle attack is an attack where the attacker is able to read, and possibly modify at will, messages between two parties without letting either party know that they have been attacked. The attacker must be able to observe and intercept messages going between the two victims. (From Wikipedia)
Man in the Middle. An attack in which the attacker sits between two hosts that are trying to communicate and intercepts all of the messages.